As one of the main advantages of using a VFD is the energy cost savings associated with speed control. When using belts, sheaves, or gearboxes to reduce speed, the motor still runs at full speed; however, a VFD reduces the actual motor speed, which reduces the amps drawn by the motor. This reduces the amount of energy used—and saves you energy costs. By ramping up the motor speed slowly, VFDs also help customers save energy by reducing the in-rush and mechanical issues associated with starting motors across the line.
VFDs and Savings
The first and most obvious way a VFD can save you money is through increasing the efficiency of your AC motors and decreasing electricity use. The amount of energy that a VFD can save depends on the average load of the motor and the number of hours per day it is turned on. While average energy savings varies, it's safe to say that most AC motors do not need to be running at full capacity for most hours of their use. Furthermore, the initial cost of a motor or VFD is generally only a fraction of the cost of operating the motor over its life span. This means that a VFD system usually pays for itself in a matter of months or years.
The University of Wisconsin-La Crosse has this example:
Consider a 25-horsepower fan motor operating for 23 hours a day. It's unlikely the fan needs to run at full capacity for the full 23 hours. If the unit runs at full capacity for two hours, 75-percent capacity for eight hours, 67 percent for eight hours, and 50 percent for five hours, a VFD would reduce energy use by 32 percent.
The other way that a VFD can save you money is through extending the life of your motor. VFDs decrease the fluid flow into an AC motor, which in turn decreases the pressure and friction on the valves and other machinery inside the motor. By running at a reduced capacity, you will also help reduce the wear and tear on your motor.
Three reasons for using a VFD
- Possible financial rebate incentives from your energy provider.
- Improved efficiency of motor-driven equipment by matching speed to changing load requirements, allowing accurate and continuous process control over a wide range of speeds.
- Yaskawa VFDs provide the benefits of network communications, a user-friendly interface, easy auto-tuning and programming, and ease of installation. Because all Yaskawa VFDs are rigorously tested, you can be assured of built-in quality and reliability.
- A VFD may be used for control of process temperature, pressure, or flow without the use of a separate controller. Suitable sensors and electronics are used to interface the driven equipment with the VFD.
- Lower maintenance costs, as lower operating speeds result in longer life for bearings and motors.
- The motor does not require a starter.
- The ability of a VFD to limit torque to a user-selected level protects driven equipment that cannot tolerate excessive torque.
- Users can utilize multi-motor applications, such as pumps or fans, with one control unit.
- High-speed applications for the wood-finishing industry.